Contractile response of horse deep dorsal penile vein to histamine

The present investigation was designed to evaluate the effect of histamine on isolated rings of horse deep dorsal penile vein. Under precontracted or basal conditions, histamine evoked an endothelium-independent contraction. Preincubation of the vein rings with the selective H1 receptor antagonist, mepyramine, shifted the concentration-response curve for histamine and to the H1 receptor agonist 2-pyridylethylamine to the right in a competitive manner. Pretreatment with cimetidine, a specific H2 receptor antagonist, did not modify the pEC50 and maximal contraction of the histamine response. Cimetidine and propranolol failed to induce a change in the relaxation caused by dimaprit, the H2 receptor agonist. Histamine contraction was unaffected by thioperamide, the specific H3 receptor antagonist. (R)-alpha-methylhistamine, the H3 receptor agonist, also induced contractions which persisted in the presence of either thioperamide or tetrodotoxin. These data indicate that horse deep dorsal penile vein shows an endothelium-independent contraction response to histamine, mainly mediated by H1 receptors.